This project will explore two major functional aspects of rhodopsin chemistry. In one, specific conformers and molecular domains of rhodopsin which are involved in the light-dependent activation of the rod GTPase and phosphodiesterase will be identified. Experiments will be carried out in reconstituted rhodopsin-phospholipid membranes and will involve the preparation of a number of chemically modified forms of rhodopsin. In the other, we shall investigate the possibility that rhodopsin has yet another basic function related to the control of transmembrane permeability and electric potential. This aspect will require the further development of a novel class of hydrophobic ion spin-labels recently introduced for the purpose of estimating transmembrane potentials. In addition to these studies directed at elucidating the function of rhodopsin, we will develop other spin label methods to investigate fundamental aspects of the electrical structure and organization of rhodopsin and photoreceptor membranes. In the course of this work, we will identify any conformeric forms of rhodopsin whose free energy is dependent on local electric potentials. The interaction of rhodopsin with specific classes of phospholipids will be investigated using spin labeling methods, 31P and 13C NMR. Of particular interest will be interdependence of rhodopsin conformation and bilayer physics and chemical features. To aid in the studies, asymmetric reconstituted membranes will be prepared.